📚 Year 9 OCR Chemistry: Quick Reference Formula & Theorem Handbook | Year 9 OCR 化学：公式定理速查手册
This handbook provides a concise summary of essential formulas, theorems, and key concepts for Year 9 OCR Chemistry. Memorise these foundations to build confidence in calculations, equations, and understanding chemical behaviour.
本手册为 Year 9 OCR 化学提供了必背公式、定理和核心概念的简明总结。熟记这些基础，能帮助你在计算、方程式和化学行为理解上建立信心。
1. Atomic Structure | 原子结构
Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons arranged in shells. The atomic number (Z) is the number of protons, which determines the element. The mass number (A) is the total number of protons plus neutrons.
原子由包含质子和中子的原子核以及分层排布的电子组成。原子序数(Z) 是质子数，决定了元素种类；质量数(A) 是质子数与中子数之和。
The number of neutrons in an atom can be found using: Number of neutrons = A – Z
原子中的中子数可通过以下公式求得：中子数 = A – Z
Electrons occupy the lowest available energy levels (shells), with the first shell holding up to 2 electrons, and the second and third shells up to 8 each.
电子先占据能量最低的电子层（壳层），第一层最多容纳 2 个电子，第二、三层最多各容纳 8 个。
2. Elements, Compounds and Mixtures | 元素、化合物和混合物
An element is a pure substance made of only one type of atom. A compound is a substance formed when two or more different elements are chemically bonded together in fixed proportions. A mixture consists of two or more substances not chemically combined, which can be separated by physical methods.
元素 是由同一种原子组成的纯物质。化合物 是由两种或以上不同元素以固定比例通过化学键结合而成的物质。混合物 由两种或以上物质组成，它们之间没有发生化学结合，可通过物理方法分离。
Key theorem: Every compound has a definite composition by mass (law of constant composition).
关键定理：每种化合物都有固定的质量组成（定组成定律）。
3. Chemical Formulae and Naming | 化学式与命名
Chemical formulae use element symbols and subscript numbers to show the ratio of atoms in a compound. For ionic compounds, the total positive charge must equal the total negative charge. Use the ‘cross-over’ method to balance charges when writing formulae.
化学式用元素符号和下标数字表示化合物中原子的比例。对于离子化合物，正负电荷总数必须相等。书写时可用“交叉”法来平衡电荷。
Examples: Sodium chloride — Na⁺ and Cl⁻ → NaCl. Magnesium oxide — Mg²⁺ and O²⁻ → MgO. Magnesium chloride — Mg²⁺ and Cl⁻ → MgCl₂.
例子：氯化钠 — Na⁺ 与 Cl⁻ → NaCl。氧化镁 — Mg²⁺ 与 O²⁻ → MgO。氯化镁 — Mg²⁺ 与 Cl⁻ → MgCl₂。
For covalent molecules, prefixes (mono-, di-, tri-) may be used, e.g. carbon dioxide (CO₂).
对于共价分子，可使用前缀（一、二、三），如二氧化碳 (CO₂)。
4. Balancing Equations and Conservation of Mass | 化学方程式配平与质量守恒
Chemical reactions are represented by word equations and symbol equations. The Law of Conservation of Mass states that no atoms are created or destroyed; the total mass of reactants equals the total mass of products.
化学反应可用文字方程式和符号方程式表示。质量守恒定律指出，原子既不能被创造也不能被消灭，反应物的总质量等于生成物的总质量。
A balanced symbol equation has the same number of each type of atom on both sides. Use coefficients (large numbers before formulae) to achieve balance. Never change the subscripts inside a formula.
配平的符号方程式两边每种原子的数目相等。通过添加化学式前的系数（化学计量数）来配平，绝不能改动化学式中的下标。
Example: 2H₂ + O₂ → 2H₂O (4 H atoms and 2 O atoms on each side).
例如：2H₂ + O₂ → 2H₂O（两边各 4 个氢原子和 2 个氧原子）。
5. Relative Atomic Mass and Relative Formula Mass | 相对原子质量与相对式量
The relative atomic mass (Aᵣ) is the average mass of an atom of an element compared to 1/12th the mass of a carbon‑12 atom. It is a ratio with no unit. Aᵣ values are shown on the Periodic Table.
相对原子质量 (Aᵣ) 是一个元素的平均原子质量与一个碳‑12 原子质量的 1/12 相比的比值，无单位。Aᵣ 数值见周期表。
The relative formula mass (Mᵣ) applies to compounds and is the sum of the Aᵣ values of all atoms in the formula.
相对式量 (Mᵣ) 适用于化合物，是化学式中所有原子的 Aᵣ 之和。
Calculation example: Mᵣ of H₂O = (2×1) + 16 = 18. Mᵣ of CaCO₃ = 40 + 12 + (3×16) = 100.
计算示例：H₂O 的 Mᵣ = (2×1) + 16 = 18。CaCO₃ 的 Mᵣ = 40 + 12 + (3×16) = 100。
6. The Mole Concept (Introduction) | 摩尔概念（入门）
A mole is the amount of substance that contains 6.02×10²³ particles (Avogadro constant). The mass of one mole of a substance (molar mass) in grams is numerically equal to its Mᵣ.
摩尔 是含有 6.02×10²³ 个微粒（阿伏伽德罗常数）的物质的量。一摩尔物质的质量（摩尔质量）在数值上等于其相对式量 Mᵣ，单位为 g/mol。
Key formula linking mass, moles and molar mass: n = m / M, where n = number of moles, m = mass in grams, M = molar mass in g/mol.
联系质量、摩尔和摩尔质量的核心公式：n = m / M，其中 n = 摩尔数，m = 质量（克），M = 摩尔质量（g/mol）。
Example: How many moles in 36 g of water? M(H₂O) = 18 g/mol, so n = 36/18 = 2 mol.
示例：36 g 水含有多少摩尔？M(H₂O) = 18 g/mol，因此 n = 36/18 = 2 mol。
7. Acids, Bases and pH Scale | 酸、碱与 pH 标度
Acids release H⁺ ions in water. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃).
酸在水中释放 H⁺ 离子。常见实验室酸有盐酸 (HCl)、硫酸 (H₂SO₄) 和硝酸 (HNO₃)。
Bases neutralise acids. Alkalis are soluble bases that release OH⁻ ions in water, such as sodium hydroxide (NaOH).
碱能中和酸。可溶性碱 在水中释放 OH⁻ 离子，如氢氧化钠 (NaOH)。
The pH scale measures the acidity or alkalinity of a solution: pH < 7 is acidic, pH = 7 is neutral, pH > 7 is alkaline. Universal indicator shows a range of colours according to pH.
pH 标度 衡量溶液的酸碱度：pH < 7 酸性，pH = 7 中性，pH > 7 碱性。通用指示剂根据 pH 显示不同颜色。
8. Neutralisation Reactions | 中和反应
Neutralisation occurs when an acid and a base react to form a salt and water. The general word equation is:
中和反应是酸与碱反应生成盐和水的过程。一般文字方程式为：
Acid + Base → Salt + Water
酸 + 碱 → 盐 + 水
Example: HCl + NaOH → NaCl + H₂O. The ionic equation for the neutralisation of a strong acid and strong alkali is: H⁺ + OH⁻ → H₂O.
示例：HCl + NaOH → NaCl + H₂O。强酸与强碱中和的离子方程式为：H⁺ + OH⁻ → H₂O。
Naming salts: hydrochloric acid produces chloride salts, sulfuric acid produces sulfate salts, nitric acid produces nitrate salts.
盐的命名：盐酸产生盐酸盐（氯化物），硫酸产生硫酸盐，硝酸产生硝酸盐。
9. Rates of Reaction | 反应速率
The rate of a reaction measures how quickly reactants are used up or products are formed. Average rate can be expressed as:
反应速率衡量反应物消耗或产物生成的快慢。平均速率可表示为：
Rate = Change in quantity of reactant or product / Time taken
速率 = 反应物或产物的变化量 / 所用时间
Factors that increase reaction rate: higher temperature, higher concentration (or pressure for gases), larger surface area of solids, and the use of a catalyst. This is explained by collision theory: particles must collide with sufficient energy (activation energy) and correct orientation.
提高反应速率的因素：升高温度、增大浓度（或气体压强）、增大固体表面积、使用催化剂。碰撞理论解释：微粒必须发生碰撞，且具有足够的能量（活化能）和正确的取向。
10. The Periodic Table and Group Trends | 周期表与族的趋势
The Periodic Table arranges elements in order of increasing atomic number. Periods are horizontal rows; groups are vertical columns. Elements in the same group have similar chemical properties because they have the same number of outer‑shell electrons.
周期表按原子序数递增排列。横行称为周期，纵列称为族。同族元素化学性质相似，因为它们的最外层电子数相同。
Key groups to remember:
需记住的主要族：
- Group 1 – Alkali metals: reactive, low density, form 1⁺ ions, reactivity increases down the group.
- 第 I 族 – 碱金属：性质活泼，密度低，形成 1⁺ 离子，向下活泼性增强。
- Group 7 – Halogens: diatomic non‑metals, form 1⁻ ions, reactivity decreases down the group.
- 第 VII 族 – 卤素：双原子非金属，形成 1⁻ 离子，向下活泼性减弱。
- Group 0/8 – Noble gases: unreactive, full outer electron shells, monatomic gases.
- 第 0/8 族 – 稀有气体：极不活泼，最外层电子全满，单原子气体。
11. Common Calculations Summary | 常见计算总结
Below is a reference table of useful equations frequently encountered in Year 9 OCR Chemistry:
以下是 Year 9 OCR 化学中经常遇到的有用公式参考表：
| Formula / 公式 | Description / 说明 |
|---|---|
| n = m / M | moles = mass ÷ molar mass / 摩尔数 = 质量 ÷ 摩尔质量 |
| Mr = Σ(Ar) | relative formula mass = sum of relative atomic masses / 相对式量 = 各原子相对原子质量之和 |
| Neutrons = A – Z | number of neutrons = mass number – atomic number / 中子数 = 质量数 – 原子序数 |
| Conc. (g/dm³) = mass (g) / volume (dm³) | mass concentration / 质量浓度 |
| Average rate = Δ quantity / Δ time | rate of reaction / 反应速率 |
| pH scale: 0–14 | acidity measure; acidic < 7, neutral = 7, alkaline > 7 |
Always check units and convert where necessary, e.g. 1 dm³ = 1000 cm³.
务必检查单位并在必要时进行换算，例如 1 dm³ = 1000 cm³。
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